Pixel structure of LCD and fabrication method thereof

ABSTRACT

In this pixel structure, a metal layer/a dielectric layer/a heavily doped silicon layer constitutes a bottom electrode/a capacitor dielectric layer/a top electrode of a storage capacitor. At the same time, a metal shielding layer is formed under the thin film transistor to decrease photo-leakage-current.

RELATED APPLICATIONS

This application claims priority to Taiwan Application Serial Number 96119417, filed May 30, 2007, which is herein incorporated by reference.

BACKGROUND

1. Field of Invention

The present invention relates to a liquid crystal display and a fabrication method thereof. More particularly, the present invention relates to a pixel structure of the liquid crystal display and a fabrication method thereof.

2. Description of Related Art

In pixel structure of a conventional liquid crystal display (LCD), the bottom electrode of the storage capacitor and the silicon island of the thin film transistor (TFT) are usually made by the same silicon layer. The top electrode of the storage capacitor and the gate electrode of the TFT are usually made by the same metal layer. Since the bottom electrode is covered by the top electrode, implanting dopants into the bottom electrode cannot be effectively performed. Therefore, the capacity of the storage capacitor cannot be effectively increased, and leakage current is easily generated when the transistor is exposed to light.

SUMMARY

In one aspect of this invention, a pixel structure of a liquid crystal display and a fabrication method thereof are provided.

A first metal layer, a first dielectric layer, and a first silicon layer are sequentially formed on a substrate. The first metal layer, the first dielectric layer, and the first silicon layer are then patterned to form an active stack and a capacitive stack respectively on an active area and a capacitive area of the substrate and to form a capacitive line connecting the capacitive stack. A gate dielectric layer and a second metal layer are sequentially formed on the substrate, the active stack, the capacitive stack, and the capacitive line stack. The second metal layer is patterned to form a gate on the active stack and a scan line connecting the gate. The silicon layer of the active stack, the capacitive stack and the capacitive line stack are heavily doped by using the gate and the scan line as a mask to form heavily doped regions. The heavily doped regions on both terminals of the silicon layer in the active stack are respectively source and drain, and the first metal layer and the heavily doped regions are respectively a first electrode and a second electrode of a storage capacitor.

A second dielectric layer is formed on the gate dielectric layer, the gate, and the scan line. The second dielectric layer is then patterned to form a first opening, a second opening and a third opening to respectively expose the drain, the source and the second electrode. A third metal layer is formed over the second dielectric layer and in the first, the second and the third openings. Next, the third metal layer is patterned to form a data line, a first conductive line connecting the data line and the source, and a second conductive line connecting the drain and the second electrode. A planar layer is formed on the second dielectric layer, the data line, the first conductive line and the second conductive line and then patterned to form a fourth opening to expose the second conductive line. A transparent conductive layer is formed on the planar layer and in the fourth opening and then patterned to form a pixel electrode connecting the second conductive line.

It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows:

FIGS. 1A-6B are diagrams showing a process for fabricating a pixel array for use in an LCD, according to a single-gate embodiment of this invention; and

FIGS. 7A-7B are diagrams showing a process for fabricating a pixel array for use in an LCD, according to a double-gate embodiment of this invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings.

Single Gate Embodiment

FIGS. 1A-6B are diagrams showing a process for fabricating a pixel array for use in an LCD, according to a single-gate embodiment of this invention.

FIG. 1A is a plan view, and FIG. 1B are cross-sectional views of sections AA′, BB′, and CC′. In FIGS. 1A-1B, a first metal layer, a first dielectric layer, and a silicon layer are sequentially formed on a substrate 100 and then patterned to form an active stack 118 a, a capacitive stack 118 b and a terminal stack 118 c respectively on an active area (section AA′), a capacitive area (section BB′), and a terminal area (section CC′). In addition, a capacitive line stack 118 d is also formed to connect the capacitive stack 118 b and the terminal stack 118 c at the same time. The material of the silicon layer can be polysilicon or amorphous silicon, for example. The material of the first dielectric layer can be silicon oxide, for example.

The active stack 118 a is obtained by stacking a metal light-shielding layer 105 a, a first dielectric layer 110 a and a silicon island 115 a. The metal light-shielding layer 105 a is made by the first metal layer, and the silicon island 115 a is made by the silicon layer. The capacitive stack 118 b is obtained by stacking a first electrode 105 b, a capacitive dielectric layer 110 b and a silicon layer 115 b. The first electrode 105 b is made by the first metal layer, and the capacitive dielectric layer 110 b is made by the first dielectric layer. The terminal stack 118 c is obtained by stacking a first terminal 105 c, a first dielectric layer 110 c and a silicon layer 115 c. The first terminal 105 c is made by the first metal layer. In FIG. 1A, the capacitive line stack 118 d above is obtained by stacking the first metal layer, the first dielectric layer and the silicon layer, and only the silicon layer 115 d on the top can be seen in FIG. 1A.

FIG. 2A is a plan view, and FIG. 2B are cross-sectional views of sections AA′, BB′, and CC′. In FIGS. 2A-2B, a gate dielectric layer 120 and a second metal layer are sequentially formed on the substrate 100, the active stack 118 a, the capacitive stack 118 b, the terminal stack 118 c and the capacitive line stack 118 d. The second metal layer is then patterned to form a gate 125 a on the active stack 118 a, a scan line 125 b connecting the gate 125 a, and a second terminal 125 c connecting the scan line 125 b. Next, the silicon island 115 a, and the silicon layers 115 b, 115 c, 115 d undergo ion implanting process to form heavily doped regions by using the gate 15 a as the implanting mask. The heavily doped regions in the silicon island 115 a serve as source 130 a and drain 130 b. The heavily doped silicon layer 115 b serves as a second electrode 130 c. The heavily doped silicon layers 115 c and 115 d are heavily doped regions 130 d and 130 e, respectively. Accordingly, the first electrode 105 b and the second electrode 130 c constitute a storage capacitor. The material of the gate dielectric layer 120 above can be silicon oxide, silicon nitride, or silicon oxynitride, for example.

Optionally, the gate 125 a with the scan line 125 b, can be further isotropically etched. Then, the reduced gate 125 a can be served as a mask for lightly doping the silicon island 115 a to form lightly doped regions 135 between the source 130 a and the drain 130 b.

In FIG. 3, a second dielectric layer 140 is formed on the gate dielectric layer 120, the gate 125 a, the scan line 125 b and the second terminal 125 c. Next, the second dielectric layer 140 is patterned to form a first opening 145 a, a second opening 145 b, a third opening 145 c and a forth opening 145 d to respectively expose the source 130 a, the drain 130 b, the second electrode 130 c, and the heavily doped region 130 d. The material of the second dielectric layer 140 can be silicon oxide, for example.

FIG. 4A is a plan view, and FIG. 4B are cross-sectional views of sections AA′, BB′, and CC′. In FIGS. 4A-4B, a third metal layer is formed on the second dielectric layer 140 and in the first opening, the second opening 145 b, the third opening 145 c and the forth opening 145 d. The third metal layer is patterned to form a data line 150 b, a third terminal 150 d at the end of the data line 150 b, a first conductive line 150 a connecting the data line 150 b and the source 130 a via the first opening 145 a, and a second conductive line 150 c connecting the drain 130 b (via the second opening 145 b) and the second electrode 130 c (via the third opening 145 c). At the same time, the second metal layer in the fourth opening 145 d and the exposed heavily doped region 130 d are removed to expose the first dielectric layer 110 c.

In FIG. 5, a planar layer 155 is formed on the second dielectric layer 140, the data line 150 b, the first conductive line 150 a, the second conductive line 150 c, the third terminal 150 d, and in the fourth opening 145 d. The planar layer 155 is then patterned to form a fifth opening 160 a to expose the second conductive line 150 c and a sixth opening 160 b to expose the first terminal 105 c.

FIG. 6A is a plan view and FIG. 6B are cross-sectional views of sections AA′, BB′, and CC′. In FIGS. 6A-6B, a transparent conductive layer is formed on the planar layer 155, and in the fifth opening 160 a and the sixth opening 160 b. The transparent conductive layer is patterned to form a pixel electrode 165 a and a protective layer 165 b on the first terminal 105 c. The material of the transparent conductive layer can be indium tin oxide, indium zinc oxide, or aluminum zinc oxide, for example.

Double Gate Embodiment

FIGS. 7A-7B are diagrams showing a process for fabricating a pixel array for use in an LCD, according to a double-gate embodiment of this invention. FIG. 7A is a plan view, and FIG. 7B are cross-sectional views of sections AA′, BB′, and CC′.

The pixel structure in double gate embodiment is structurally identical (e.g. elements shown in sections BB′ and CC′) to the pixel structure disclosed in single gate embodiment. The only difference is that transistor in the single-gate pixel structure possess single gate, while the transistor in the double-gate pixel structure possess double gates (shown in section AA′). Therefore, elements in double gate embodiment (FIGS. 7A-7B) identical to those in single gate embodiment (FIGS. 1A-6B) are numbered identically. Furthermore, since the process for fabricating the double-gate embodiment is basically the same as the process for fabricating the single-gate embodiment, the detailed descriptions of the double-gate embodiment is omitted and only the transistor's structure is discussed below.

In FIG. 7A, the active stack 118 a of the transistor is bent to overlap with the gate 125 a and the scan line 125 b to form a double gate structure. In section AA′ of FIG. 7B, gate 125 a, overlapped portion of the scan line 125 b, source 130 a, drain 130 b, and heavily doped region 130 f constitute the double-gate transistor. In addition, lightly doped regions 135 can be formed on both sides of the gate 125 a and the overlapped portion of the scan line 125 b.

Accordingly, the bottom electrode, i.e. the first electrode 105 b, of the storage capacitor is made by metal, and the upper electrode, i.e. the second electrode 130 c, is made by heavily doped silicon layer. Hence, compared with a conventional capacitor composed of non-doped silicon layer, gate dielectric layer, and metal, the storage capacity is greatly increased. Moreover, a metal light-shielding layer is under the transistor to reduce the light-induced leakage current.

It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims. 

1. A pixel structure of a liquid crystal display, the pixel structure comprising: a thin film transistor on an active area of a substrate, the thin film transistor comprises: an active stack composed of a metal light-shielding layer, a dielectric layer and a silicon island, wherein the silicon island has source and drain on two ends thereof; a gate dielectric layer on the active stack; and at least a gate on the gate dielectric layer over the active stack; a storage capacitor, having a first electrode, a capacitive dielectric layer and a second electrode from bottom to top, on a capacitive area of the substrate, wherein the first electrode and the metal light-shielding layer are discontinuous and separated from each other and are made of a first metal layer, the capacitive dielectric layer and the dielectric layer are discontinuous and separated from each other and are made of a first dielectric layer, the second electrode and the silicon island are made of a same single silicon layer and are discontinuous and separated from each other, and the second electrode is a heavily doped silicon layer and connects the drain; and a pixel electrode connecting the second electrode.
 2. The pixel structure of claim 1, further comprising two lightly doped regions between the source and the drain.
 3. The pixel structure of claim 1, further comprising: a scan line electrically connecting the gate; a second dielectric layer over the gate dielectric layer, the gate and the scan line; a data line on the second dielectric layer; a first conductive line on the second dielectric layer and connecting the data line and the source; and a second conductive line on the second dielectric layer and connecting the second electrode to the pixel electrode.
 4. The pixel structure of claim 3, further comprising: a capacitive line stack electrically connecting the storage capacitor, wherein the structure of the capacitive line stack is the same as the structure of the storage capacitor; a first terminal at an end of the capacitive line stack, wherein the first terminal is made of the first metal layer; and a protective layer on the first terminal, wherein the protective layer and the pixel electrode are made of a same transparent conductive layer.
 5. The pixel structure of claim 4, further comprising a second terminal on an end of the scan line and a third terminal on an end of the data line.
 6. The pixel structure of claim 5, wherein the scan line, the gate, and the second terminal are made of a second metal layer, and the data line, the first conductive line, the second conductive line and the third terminal are made of a third metal layer.
 7. The pixel structure of claim 3, wherein a portion of the scan line locates on the active stack.
 8. The pixel structure of claim 1, wherein the silicon layer is made from polysilicon or amorphous silicon.
 9. The pixel structure of claim 3, wherein the first and the second dielectric layer are made from a material comprises silicon oxide.
 10. The pixel structure of claim 4, wherein the transparent conductive layer is made from indium tin oxide, indium zinc oxide, or aluminum zinc oxide.
 11. A pixel structure of a liquid crystal display, the pixel structure comprising: a thin film transistor on an active area of a substrate, the thin film transistor comprises: an active stack composed of a metal light-shielding layer, a dielectric layer and a silicon island, wherein the metal light-shielding layer, the dielectric layer and the silicon island have the same pattern, and the silicon island has source and drain on two ends thereof; a gate dielectric layer on the active stack; and at least a gate on the gate dielectric layer over the active stack; a storage capacitor, having a first electrode, a capacitive dielectric layer and a second electrode from bottom to top, on a capacitive area of the substrate, wherein the first electrode and the metal light-shielding layer are discontinuous and separated from each other and are made of a first metal layer, the capacitive dielectric layer and the dielectric layer are discontinuous and separated from each other and are made of a first dielectric layer, the second electrode and the silicon island are made of a same single silicon layer and are discontinuous and separated from each other, and the second electrode is a heavily doped silicon layer and connects the drain; a scan line electrically connecting the gate; a second dielectric layer over the gate dielectric layer, the gate and the scan line; a data line on the second dielectric layer; a first conductive line on the second dielectric layer and connecting the data line and the source; and a second conductive line on the second dielectric layer and connecting the second electrode to the drain; and a pixel electrode connecting the second conductive line.
 12. The pixel structure of claim 11, further comprising two lightly doped regions between the source and the drain.
 13. The pixel structure of claim 11, further comprising: a capacitive line stack electrically connecting the storage capacitor, wherein the structure of the capacitive line stack is the same as the structure of the storage capacitor; a first terminal at an end of the capacitive line stack, wherein the first terminal is made of the first metal layer; and a protective layer on the first terminal, the protective layer and the pixel electrode being made of a same transparent conductive layer.
 14. The pixel structure of claim 13, further comprising a second terminal on an end of the scan line and a third terminal on an end of the data line.
 15. The pixel structure of claim 14, wherein the scan line, the gate, and the second terminal are made of a second metal layer, and the data line, the first conductive line, the second conductive line and the third terminal are made of a third metal layer.
 16. The pixel structure of claim 11, wherein a portion of the scan line locates on the active stack.
 17. The pixel structure of claim 11, wherein the silicon layer is made from polysilicon or amorphous silicon.
 18. The pixel structure of claim 11, wherein the first and the second dielectric layer are made from a material comprises silicon oxide.
 19. The pixel structure of claim 13, wherein the transparent conductive layer is made from indium tin oxide, indium zinc oxide, or aluminum zinc oxide. 